I've got a repair in right now which is different kind of car but it is sparking big time and it appears to be a design flaw. MTH Smoking tank car where the pick arms going to the roller have too much play and they touch the side of the truck causing a intermittant spark.
I've also seen numerous Railking SD-70 engines where the center rail pickup wire wears going thru the shell since MTH doesn't protect their very thin wire from rubbing on the metal.
Jim